VTOL is an abbreviation for Vertical
Take-Off and Landingaircraft. See also V/STOL. This classification
includes fixed-wing aircraft that can hover,
take off and land vertically as well as helicopters and other aircraft with powered
rotors, such as tiltrotors.[1][2][3][4]Autogyros, balloons, airships and rockets are not normally considered VTOL, but
may be termed VTVL (Vertical Takeoff with Vertical Landing). Some
VTOL aircraft can operate in other modes as well, such as CTOL (Conventional Take-off and
Landing), STOL (Short Take-Off and
Landing), and/or STOVL (Short
Take-Off and Vertical Landing) mode. Others, such as some
helicopters, can only operate by VTOL, due to the aircraft lacking
landing gear that can handle horizontal
motion. VTOL is a subset of V/STOL.

Besides the ubiquitous helicopter, there are currently two types
of VTOL aircraft in military service: craft using a tiltrotor, such as the BellBoeingV-22 Osprey, and aircraft using directed
jet thrust such as the Harrier family.

Contents

History

In addition to the helicopter, many approaches have been tried
to develop practical aircraft with vertical take-off and landing
capabilities. An early contribution to VTOL was Rolls-Royce's Thrust Measuring Rig
("flying bedstead") of 1953. This led to the first VTOL engines as
used in the first British VTOL aircraft, the Short SC.1 (1957) which used 4 vertical lift
engines with a horizontal one for forward thrust.

The use of vertical fans driven by engines was investigated in
the 1950s. The US built an aircraft where the jet exhaust drove the
fans, while British projects not built included fans driven by
mechanical drives from the jet engines.

The idea of using the same engine for vertical and horizontal
flight by altering the path of the thrust led to the Bristol Siddeley Pegasus engine which used
rotating ducts to direct thrust over a range of angles. This was
developed side by side with an airframe, the Hawker P.1127, which became subsequently
the Kestrel and then entered production as the Hawker Siddeley Harrier, though
the supersonic Hawker Siddeley P.1154 was
canceled in 1965. The French in competition with the P.1154 had
developed a version of the Dassault Mirage III capable of
attaining Mach 1. The Dassault Mirage IIIV achieved
transition from vertical to horizontal flight in March 1966,
reaching Mach 1.3 in level flight a short time later.

NASA has flown other VTOL craft
such as the Bell XV-15
research craft (1977), as have the Soviet Navy and Luftwaffe. Sikorsky tested an aircraft dubbed the X-Wing, which took
off in the manner of a helicopter. The rotors would become
stationary in mid-flight, and function as wings, providing lift in
addition to the static wings. Boeing X-50 is a Canard
Rotor/Wing prototype that utilizes a similar concept.

The Yakovlev
Yak-38 was the Soviet Navy's VTOL aircraft for their light
carriers, cargoships, and capital ships. It was developed from the
Yakovlev
Yak-36 experimental aircraft. Before the Soviet Union
collapsed, a supersonic VTOL aircraft was developed as the Yak-38's
successor, the Yak-141, which never went into
production.

In the 1960s and early 70s Germany planned three different VTOL
planes. One used the F-104 as a base for research for a V/STOL
aircraft. Although two models (X1 and X2) were built, the project
was canceled due to high costs and political problems as well as
changed needs in the Luftwaffe and NATO. The EWR VJ 101C did perform free VTOL take-offs
and landings, as well as test flights beyond mach 1 in the mid- and
late 60s. One of the test-aircraft is preserved in the Deutsches
Museum in Munich, Germany. The others were the VFW-Fokker VAK 191B light
fighter and reconnaissance plane, and the Dornier Do 31E-3 (troop) transport.

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Canadair
CL-84 Dynavert

The CL-84
was a Canadian V/STOL turbine tilt-wing monoplane designed
and manufactured by Canadair between 1964 and 1972. The Canadian
government ordered three updated CL-84s for military evaluation in
1968, designated the CL-84-1. From 1972 to 1974, this version was
demonstrated and evaluated in the United States aboard the aircraft
carriers USS Guam and USS Guadalcanal, and at
various other centres. These trials involved military pilots from
the United States, the United Kingdom and Canada. Two of the CL-84s
crashed due to mechanical failures, but no loss of life occurred as
a result of these accidents. No production contracts resulted.

Aircraft designed to operate in extraterrestrial environments
often utilize VTOL. An example of this type of aircraft is the LLRV. Spacecraft typically
operate in environments where runways or even a suitably flat
surface for skids is nonexistent.

V-22

The V-22 Osprey
is the world's first production tiltrotor aircraft, with one three-bladed proprotor, turboprop engine, and
transmission nacelle mounted
on each wingtip. The Osprey is a multi-mission aircraft with both a
vertical takeoff and landing (VTOL) and short takeoff and landing
capability (STOL). It is designed
to perform missions like a conventional helicopter with the long-range, high-speed
cruise performance of a turboprop aircraft. The FAA classifies the
Osprey as a model of powered lift aircraft.